In the displays represented by liquid crystal displays and organic EL displays, insulation films, semiconductor films, etc. are successively deposited on a glass substrate (also called a first substrate or an array substrate) through the chemical vapor deposition (CVD) or the like method and subjected to the same steps as fabricating semiconductor integrated circuits, and then a microelectronic device, such as a thin film transistor (TFT) etc., is formed in the vicinity of each of pixels constituting a display screen. By controlling on-off operation and light and shade of each pixel with this microelectronic device, a display image is constituted. That is to say, in fact, the active devices, such as TFTs etc. are fabricated directly on the glass substrate used, in fact, for a planar display. However, it is intended to enlarge the display area to reply to a recent demand for display screen enlargement, the following problems have been raised.
The first problem is that the fabrication device, such as CVD device etc. for fabricating microelectronic devices on a planar display substrate, has to be inevitably enlarged with the enlargement of a planar display. In addition, since many steps are required for fabricating the microelectronic device, a plurality of the aforementioned enlarged fabrication devices are required and a clean room for installing these fabrication devices has to be enlarged. As a result, it is difficult to reduce the fabrication cost.
The second problem is that since an amorphous silicon (a-Si) film etc. that can be fabricated from a thin film that can be deposited at low temperature of around 300° C. the glass substrate can endure is used as a semiconductor film, the operation performance is inferior to that of semiconductor electronic devices using crystallized silicon. To solve the inferior operation performance, studies have been made on the fabrication of a TFT enhanced in mobility and consequently enhanced in operation performance through the steps of melting the deposited a-Si to form polysilicon (poly-Si) film and using the poly-Si film. Particularly in the display according to an organic EL that emits light by application of individually controlled electric currents through the respective pixels, it is generally confirmed that the operation performance of the a-Si TFT is insufficient. In view of this, expectation of a laser-melted poly-Si film is heightened. However, since it highly costs to fabricate a laser-melted poly-Si film, it is premised that the application thereof is only in a restricted range. Also in an a-Si TFT that has a display screen diagonal dimension of 40 inches or more, an a-Si film deposition step and the following pattern transfer step are difficult to take, and the cost for taking the steps becomes increased.
The third problem is that in displays using a glass plate as a substrate, when the display screen size is in the range of 40 to 100 inches, the thickness of the glass substrate has to be large enough to attain its sufficient strength. This increases the entire display device weight and consequently requires a device structure to be enlarged in order to stably install the display device and raises the entire cost.
The technique of fabricating a plurality of microelectronic devices, such as TFT etc., in advance on a substrate other than a glass substrate and mounting the fabricated microelectronic devices at a predetermined position on a glass substrate is disclosed. (Refer to Non-patent Document 1 and Patent Documents 1 and 2, for example.)    Non-patent Document 1: “Application of Fluidic Self Assembly ™ Technology to Flat Panel Displays” edited by Anne Chiang, IDW 2000 Letters, ITE, published by SID, Nov. 29, 2000, pp. 195-198    Patent Document 1: JP-A HEI 11-142878    Patent Document 2: JP-A 2002-244576
Non-patent Document 1 discloses a method of preparing a mold for fitting pixel control devices (microelectronic devices) onto a flat panel display substrate and mounting a great number of pixel control devices prepared in advance at a different place onto the mold by pouring them together with a liquid. However, since the ratio of the number of the pixel control devices successfully fitted into the mold on the display substrate to the number of the pixel control devices poured together with the liquid is small, the prior art method is not put to practical use. Furthermore, since a great number of pixel control devices are poured onto the display substrate in view of the small ratio, excess pixel control devices not fitted into the mold have to be recovered. Moreover, since the pixel control devices when being poured together with the liquid and recovering the excess pixel control devices move directly in contact with the display substrate, there is a fair possibility of the pixel control devices damaging the display substrate.
On the other hand, in Patent Document 1, disclosed is a method of forming pixel control devices on a silicon substrate in relation to the pitch of array on a planar display substrate, forming recesses for fitting the pixel control devices (microelectronic devices) therein at positions of the display substrate to which the selected devices are transferred, position-aligning the devices on the silicon substrate relative to the display substrate and irradiating the devices with ultraviolet rays, thereby selectively weakening the adhering force between the pixel control devices to be transferred and the display substrate by an adhesive to fit the pixel control devices into the recesses in the display substrate. This prior art also discloses a method of forming an adhesive layer in each of the recesses and fixing the pixel control devices in the recesses.
To fit the pixel control devices in the recesses, it is necessary to form the recesses slightly larger than the pixel control devices. This size difference causes displacement of the pixel control devices in the recesses, resulting in making the subsequent wiring step difficult to conduct. When the size difference is made small to prevent the disadvantage from occurring, there is a possibility of slight positional displacement causing the pixel control devices to be fitted in the recesses in an inclined fashion. Therefore, formation of the recesses and positioning of the pixel control devices have to be conducted with extremely high precision. This is not realistic. In addition, in the case of fixing the pixel control devices in the recesses with adhesive layers formed therein, if the adhesive layers should ooze when adhering the pixel control devices adhere fast to the adhesive layers, there would be a possibility of the adjacent pixel control devices being adhered to the oozed adhesive layers. To avoid this, an extremely small amount of the adhesive has to be applied to extremely accurate positions, resulting in much higher cost.
As described above, Non-patent Document 1 has a problem in low ratio of success in disposing the pixel control devices on the display substrate and requires the excess pixel control devices not disposed to be removed and recovered, resulting in a method not capable of reducing the fabrication cost. Furthermore, the removal and recovering of the excess pixel control devices possibly damage the display substrate.
On the other hand, in the technique of Patent Document 1, there is a possibility of the pixel control devices being displaced in the recesses or being fitted aslant in the recesses due to the size difference between the pixel control devices and the recesses. To avoid this, positioning has to be performed with extremely high accuracy and, as occasion demands, it will be necessary to confirm the state of displacement one by one. Thus, the cost reduction cannot be attained. Furthermore, in the case of forming adhesive layers in the recesses, to prevent the adhesive layers from oozing, the amount and position of application of the adhesive layers has to be controlled with high accuracy. This is also a cause of high cost. Furthermore, in order to selectively weaken the adhesion force between the pixel control devices to be transferred and the display substrate by the adhesive layer through irradiation with ultraviolet rays, since it is difficult to irradiate the ultraviolet beams in the same shape as the pixel control devices, it can be assumed that the ultraviolet beams having a diameter larger than the shape of the pixel control device are irradiated onto the devices. In this case, the adhesion force by the adhesive layer will become weak gradually from around non-selected pixel control devices adjacent to the selected pixel control devices. In particular, the adhesion force to pixel control devices delay in the order selected is made weak before being selected. This causes positional disturbance of the non-elected pixel control devices to produce positional deviation and falling of the devices. In Patent Document 1, since the pixel control devices are irradiated with ultraviolet rays in the state, with all the pixel control devices upside down, there is a fair possibility of the devices falling off. This is a serious problem.
In the pixel control devices for controlling a plurality of pixels, it has been desired to efficiently wire these devices even after mounting the devices on the planar display substrate. However, the conventional wiring method comprises the steps of depositing wiring material on the entire surface of a substrate in the form of a thin film, pattern-transferring the deposited film using the photolithography method, etching the thin wiring material film and removing a resist film. These steps have incurred highly expensive and been complicated ones.
Furthermore, in almost all liquid crystal displays displaying an active matrix, one pixel (pixel electrode) and one pixel control device (TFT) are generally disposed at each intersection of longitudinal and lateral wirings (the longitudinal wiring being a source wiring and the lateral wiring being a gate wiring), and the TFT serves as a switching device for controlling a single pixel. Since the wiring portion in the display functions as a light-blocking portion, when there are plural wiring portions, there are limitations on enhancement of the aperture ratio. In Patent Document 2, as shown in FIG. 38, at the center of four pixels arranged in such a manner that two upper ones and two lower ones are across a lateral wiring and that two left ones and two right ones are across a longitudinal wiring, four thin film transistor devices 12 are densely disposed for controlling the four pixels. It seems to the inventors that the four thin film transistor devices 12 constitute an aggregation of devices for controlling the pixels on the peripheries of the devices, respectively. (The aggregation is called “a device block 13” in Patent Document 2.) However, in view of the aspect of the wirings used in common with each other while the pixel control devices are concentrated at the center of the four pixels, it is only conceived that a pixel control device controls a pixel adjacent thereto. Furthermore, in the method of Patent Document 2, since the devices are disposed at a two-pixel pitch, a light-shielding portion that constitutes a wiring portion exists at a two-pixel pitch. In this case, since colors are separate every two colors, such as RG, BR, GB or RG, the color phenomena are problematic. It is desirable to separate colors every three colors of RGB. In Patent Document 2, however, there gives rise to a color mixture with the color of the adjacent pixel that adversely affects a color contrast.
In view of the foregoing, an object of the present invention is to provide a pixel control device selection transfer method for selectively transferring pixel control devices for controlling a plurality of pixels precisely onto a planar display, such as a liquid crystal display, an organic EL display, etc. with ease at low cost without inducing any positional deviation, provide a mounting apparatus for mounting the pixel control devices used in the pixel control device selection transfer method, provide a wiring formation method performed after the transfer of the pixel control devices for efficiently wiring the pixel control devices at low cost and provide a planar display substrate that can realize reduction of the number of the wirings (wiring number reduction capability), makes it possible to reduce the area of light-blocking portions resulting from the wiring formation and excels in color phenomena and color contrast.